Vehicle powertrains are often equipped with exhaust gas oxygen sensors for monitoring an oxygen content of exhaust gases in a vehicle exhaust conduit. Various types of exhaust oxygen sensors are known, including but not limited to universal exhaust gas oxygen (UEGO) sensors. Unlike some exhaust gas sensors that merely indicate a presence or absence of oxygen, UEGO sensors provide an output that is proportional to the concentration of oxygen in the exhaust gas, and thereby allow a ratio of air and fuel supplied to the vehicle engine to be monitored.
However, UEGO sensors may show a large variability in output during lean air/fuel conditions (i.e. during periods of high exhaust oxygen content), and/or with aging. Furthermore, UEGO sensors may show significant drift during periods of elevated exhaust temperature and/or exhaust pressure, for example, during particulate filter regeneration. Improper performance of a UEGO sensor may lead to improper engine operation, as an engine controller may use an output of a UEGO sensor to adjust amounts of air and fuel provided to an engine as driving conditions change.
Therefore, in one approach, problems with the consistency of an oxygen sensor output may be at least partially addressed in an apparatus comprising an internal combustion engine, an exhaust oxygen gas sensor and a particulate filter by determining a first air/fuel ratio from a signal from an exhaust oxygen sensor; determining a second air/fuel ratio from a temperature upstream of the particulate filter, a pressure differential across the particulate filter and one or more of an airflow into the engine and a fuel flow into the engine; comparing the first air/fuel ratio and the second air/fuel ratio; and diagnosing an error condition of the oxygen sensor if the first air/fuel ratio does not meet a predetermined condition relative to the second air/fuel ratio. In this manner, the use of erroneous output of an oxygen sensor to adjust an engine operating condition may be avoided.